Electrical musical instrument



1936- E. D. LILJA ELECTRICAL MUSICAL INSTRUMENT 6 Sheets-Sheet l INVENTOR ATTORNEYS Aug. 4; 1936. L|LJA 2,049,616

EIZECTRICAL MUSICAL INSTRUMENT Filed May 18, 1933 6 Sheets-Sheet 2 I] INVENTOR F) Edgar Liya WI t ATTORNEY-5 g 4, 1936- ,E. D, LILJA I ELECTRICAL MUSICAL INSZQUMENT Filed May 18, 1933 l e Sheets-Sheet 3 pLALA K L01 ATTORNEYS INVENTO R Ed ar 1). Lil 'a BY 3 J II... I)

llll L Au 4, 1936. E D LJA 2,049,616

\ ELECTRICAL MUSICAL INSTRUMENT Filed m y 18, 1955- s Sheets-Sheet 4 F 8 6y. am: CYCLE, J

'7 F 4 i F a 1 INVENTOR Edgar l). Lil/a BY KHAN ATTORNEYS Aug. 4, 1936. D l JA 2,049,616 v ELECTRICAL MUS ICAL INSTRUMENT Filed May 18, 1935 6 Sheets-Sheet 5 INVENTOR E0150 r' 11 L i l/a ATTORNEYS Patented Aug. 4, 1936 UNITED STATES PATENT OFFICE 28 Claims. v

This invention relates to improvements in electrical musical instruments and more particularly to an instrument in which different notes are produced by vibration of a resonant body in accordance with the wave form of an alternating electric voltage.

The general object of the present invention is to provide a novel musical instrument of the above character by which a large number of notes of the tempered scale may be produced by means of equipment which is more compact and much less expensive to manufacture than ordinary keyboard controlled instruments now in common use.

Another object is to provide for the production through electromagnetic action of a large number of notes in a wide variety of different tone qualities without materially increasing the cost of the manufacture of the instrument as a whole.

A further object is to provide a novel alternator for generating the alternating voltages by which the notes of different pitch are produced.

Still another object is to provide a novel electric circuit arrangement for enabling the alternating voltages to be applied under keyboard control to the sound-producing apparatus.

The invention also resides in the novel manner of producing the different tone qualities and in the construction which permits of a wide variation in tone qualities obtained without adding materially to the cost of manufacture.

Another object is to provide a novel means for producing a tremolo effect in an instrument of the above character.

Other objects and advantages of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings, in which Figure 1 is a perspective view of a console for controlling a musical instrument embodying the features of the present invention.

Fig. 2 is a fragmentary perspective view illustrating the manner in which the keys of the console are utilized to control the instrument.

Fig. 3 is an elevational view of the apparatus for generating the alternating voltages.

Fig. 4 is a plan view of the mechanism shown in Fig. 3. I

Fig. 5 is an enlarged elevational view of a group of the alternators.

Fig. 6 is a sectional view taken along the line 6-4 of Fig. 5.

Fig. 7 is a fragmentary sectional view taken along the line 1-1 01' Fig. 6.

-Figs.8, 9 and show different types of pickup core constructions.

Figs. 8, 9 and 10 are charts showing the wave forms of the alternating voltages by the pick-up core constructions shown in Figs. 8, 9 and 10. 5

Fig. 11 is a fragmentary view similar to Fig. 7 illustrating a modified form of the invention.

Fig. 12 is a fragmentary side view of one of the pick-up cores shown in Fig. 11.

Fig. 13 is a cross-sectional view through one 10 of the stops of the console.

Fig. 14 is a schematic view or wiring diagram of a part of the musical instrument.

Fig. 15 is a fragmentary view and wiring diagram illustrating the manner of controlling the 15 instrument from dilierent keyboards.

The musical instrument shown by way of iilustration in the drawings comprises generally an audio-frequency generator controllable selectively as from the keyboard of a console (Fig. 1) and operable to generate alternating voltages of different frequencies and wave forms which are impressed upon the input circuit of a vacuum tube amplifier l6 (Figs. 14 and 15) the construction of which is well known in the art and the output 1 from which is delivered to a loud speaker ll (Figs. 1 and 14) having a vibrating body which reproduces acoustically the voltage wave forms produced by the generator. The frequency generator comprises essentially a plurality of electromagnetic pick-up coils i8 (Figs. 4, 6 and 14) in which voltage pulsations are induced at the different tone frequencies by varying the reluctance of constantly energized magnetic circuits through cores I 9, such variations being produced by moving across the ends of the cores a magnetic member 20 having alternately arranged sections of high and low reluctance.

In the illustrated embodiment, the instrument is similar, as regards mode of control, to an ordi- 40 nary pipe organ, the different notes being sounded in,response to the depression of the keys 2| and 22 of two keyboards known as the great manual and the swell ,manual and to depression of pedals ber of notes with different tone qualities, the pick-up coils 18 are arranged in a. plurality of groups (Figs. 3 and 4), the coils of each group being common to one of a plurality of rotary disks which constitute the movable reluctance varying members 20 above referred to. In the present instance, two-pick-up coils are employed for producing each note and these coils are mounted on the two magnetic cores l9 (Figs. 3 to 6) which are mounted in axial alinement on opposite sides of one of the disks 20 with their adjacent ends disposed closely adjacent and facing the disk. The remote ends are screw-threaded, for purposes of adjustment of the width of the gaps 25, into stationary plates 26 of magnetic material and jointed externally of the disk by bars 21. To set up magnetic flux in the magnetic circuit through the plates 26, bars 21, the cores i9 and the air gap 25 between the latter, bars 21 are permanently magnetized. If desired, the cores l9 may also be magnetized. The amount of flux threading this circuit will be a function of the reluctance of the air gap 25 which may be varied in width by adjusting the cores l3.

Variation in the reluctance of the magnetic circuits above referred to at frequencies producing the different notes is accomplished in the present instance by perforating the disks 23 with closely spaced holes 28 arranged in concentric circles or rows which are disposed opposite the faces of different pairs of the cores 19. While the holes may be of various cross-sectional shapes, as will appear later, it is preferred, for the sake of simplicity in the manufacture of the disks, to employ circular holes. In the rotation of each disk 23, each row of holes is moved through the air gap 25 between one pair of the cores l9 causing the reluctance in the magnetic circuit therethrough to be varied from a maximum value when one of the holes is alined with the cores to a minimum value when the iron between two adjacent holes is disposed in the magnetic circuit. Thus. as the disk rotates, the reluctance of the magnetic circuit through each pair of pick-up cores will be changed alternately from maximum to minimum value at a frequency determined by the number of holes passing through the air gap per second.

The magnetic flux threading any pair of the pick-up cores increases and decreases alternately as the reluctance of the circuit decreases and increases while the holes move through the air gap 25. As a result of these flux changes, an alternating voltage having the same frequency as the flux changes is induced in the coils linking the cores. By impressing this voltage upon the input circuit of the amplifier l6, sound of a pitch determined by the frequency of the voltage pulsations will be produced by the loud speaker IT.

The disks 20 are fast upon shafts 30, 3|, 32 and 33 rotatably mounted in spaced bearings 34 and driven from a common synchronous alternating current motor 35 through the medium of a shaft 36 and speed-reduction gear trains 31. By employing the proper gearing, the shafts may be driven at any desired speeds. It will be observed that the frequency of the voltage pulsations in the coils i8 is determined by the speed of rotation of the disk 20, the radial position of the cores l9, and the circumferential spacing of the holes 28.

By employing two cores IQ for each note arranged on opposite sides of a disk 20, it will be apparent that the reluctance of the magnetic circuit through the cores is not varied by lateral wobbling of the disk due to slight inaccuracies in the disk and its mounting. By the use of a coil IE on each of the two cores and connection of these coils in proper series relation. the effect of disk wobble on the total flux linkage is further minimized. Any tremolo in the musical note produced is thus effectually avoided.

While the pick-up coils l8 may be rendered operative in various ways to produce any one or more of the corresponding notes, this is accomplished herein by the use of switches actuated selectively by manipulation of the keys of the console. Herein the keys and also the pedals are of a construction similar to that used in pianos and organs comprising an elongated bar 38 Fig. 2) pivoted at 39 and adapted to be depressed against the action of a light spring 43 acting downwardly on the rear end of the key and supported between clamping bars 4|.

For a purpose to appear presently, it is preferred that all of the pick-up coils l8 oi the instrument which are active at any time be connected in series relation in the input circuit of the amplifier. To permit of this arrangement, each key 38 and pedal 23 of the console is arranged to actuate a switch 42 hereinafter referred to as the by-pass switch and a switch 43 hereinafter referred to as the sounding switch. The switches have a common terminal carried by the spring arm 40 and insulated terminals on spring strips 44 and 45 anchored by the bars 4| on opposite sides of the spring 40. The strips are more flexible than the spring 40 and so stressed that they normally tend to move toward the spring, the extent of such movement being determined by stop flanges 46 and 41. When the key is in normal position Fig. 2), the by-pass switch 42 is held closed by the spring 40. key is depressed. the strip 44 follows the spring 40 upwardly, the spring contact engaging the contact of the strip 45 to close the sounding switch 43 before the strip 44 engages the stop 46 to open the switch 42. key, the by-pass switch closes before the strip 45 engages the stop 4! to open the switch 43.

As the 1:

Upon release of the To enable certain notes to be sounded from a plurality of the keyboards as will appear later,

additional sets of by-pass and sounding switches may be associated with the keys.

The manner of utilizing the switches 42 and 43 to connect the different pick-up coils in series relation in the output circuit of the amplifier i6 is illustrated in Fig. 14 which, for the sake of simplicity, shows three sets of the pick-up coils, these being numbered l8, I8 and I8 The circuit extends from the amplifier through a conductor 48 having a manually controllable switch 49 therein to the common contact 40 of one set of key controlled switches 42 and 43 the switch 42 being normally closed. The other contact of this switch is connected to a conductor 50 which forms a by-pass around the switch 43 and the coils Ill and extends to the common contact sponding conductor 50 and the other terminal is joined to the contact 45 of the sounding switch 43 through a conductor 53 having a switch 54 interposed therein for a purpose to appear presently. Assuming that all of the switches 54 are closed, it will be apparent that any one of the pick-up coils may be thrown into the amplifier circuit by depressing the key which closes the proper sounding switch 43 and opens the associated by-pass switch 42 whereupon a note of the pitch determined by the frequency of the pick-up coil pulsations will be produced by the loud speaker I1. If a plurality of keys are depressed simultaneously, a corresponding number of coils will be included in the circuit and a note produced which is the composite of the notes produced by the individual coils then connected in the circuit.

It will be apparent that the pick-up coils might be connected permanently in the amplifier input circuit and rendered ineffectual simply by establishing short-circuits around them. But the double switch arrangement above specified is preferred because the coils are out of circuit when inactive and any possibility of notes being sounded due to high resistance at the key contacts is eliminated. In view of the order in which the switches 42 and 43 operate upon depression and release of the keys. it will be apparent that the input circuit of the amplifier is always maintained closed during manipulation of the keyboard. The possibility of interrupting the notes which are to be held during depression or release of a key is thus avoided.

I The principal reason for arranging the pick-up coils for connection in series relation is to elimidifferent tone qualities is reduced to a minimum. In addition, the

'trolling the tone quality of the notes.

nate the loss due to the circulating currents which flow in parallel connected coils. wiring required to accommodate a large number of different keys and stops is reduced to a minithree rows 28 28 and 28 spaced respectively Connected in parallel with the group of pickup coils and by-pass conductors for any one keyboard is a variable resistance shunt 55 which may be adjusted to vary the volume of the sounds produced. A condenser 56 located in the same relation to the pick-up coils cooperates wi th the inductance coil 5| to form a filter for reducing the voltage transients impressed upon the amplifier and consequent loud speaker noise due to operation of the switches.

When sounds are produced in the manner above described: the wave form of the voltage pulsations and therefore the quality of the tone produced is determined by three factors, namely, the relative sizes of the holes 28 in the disks 20, the shapes of these holes relative to those of the ends of the cores l9, and the size of the air gap through which the disk rotates. Thus by varying these factors in different ways, the wave form of the sound may be changed so as to produce tone qualities simulating different kinds of musical instruments.

For example, Figs. 8, 9 and 10 and the associated charts illustrate the different tone qualities which may be obtained by varying the crosssectional shape of the ends of the cores I9. In each of these instances, the cores are of inch permanently magnetized cobalt steel and the disk is of soft steel having holes of an inch in diameter spaced from the axis of the disk the same distance as the cores. With a core of square cross-section as shown in Fig. 8 spaced .015 of inch from the disk, the wave form of the voltage very closely approximates a true sine wave profcores and pick-up coils employed. the number and complexity of the disks required ducing a tone similar in quality to that of a tuning fork. With the round core shown in Fig. 9 spaced .004 of an inch from the disk, the quality of the tone produced is similar to that produced in a pipe organ with the diapason and the flute stops active. In Fig. 10, the core is tapered at its end to a diameter of of an inch and spaced .004 of an inch from the disk. This arrangement produces a peaked wave yielding a note similar to that of the violin. Thus, it will be apparent that by employing cores of different cross-sectional shapes, the desired variations in the tone qualities may be obtained simply and conveniently.

An important advantage of employing pick-up cores of different shapes in order to produce different tone qualities is that the holes in the disks 20 may be made of round shape and therefore punched readily from sheet metal. Moreover, since different tone qualities are obtainable with holes of the same shape, one row of holes may serve to produce all of the different tone qualities of the same pitch. For this purpose, the cores for the different tone qualities are arranged in annularly spaced relation around the disk as in the case of the cores I9 I9 I9 l9 and I9 shown in Fig. '7. Thus a disk having ten concentric rings of holes with five sets of cores for each ring would contribute notes of ten different pitchesand five different qualities for each pitch. The number of different qualities which may be obtained is limited only by the circumferential length of the ring of holes and the sizes of the In this way,

to produce any required number of ptches of Fig. 11 illustrates still another method of con- In this instance, the holes for each note are arranged in according to the frequency of the fundamental note, that of the first harmonic, that is, one octave above the fundamental, and the second harmonic, that is, a fifth above the first harmonic. Associated with these holes are five pickup cores 51, 58, 59, 60 and 5| for producing different tone effects. The core 51 has a face which overlies all three rows of holes and therefore produces a note containing the fundamental and I up cores having faces of various shape in order to produce still other tone qualities.

It is contemplated that the pick-up coils by which different tone qualities are obtained may be associated with the control keys selectively by positioning of the stops 24 (Fig. 1) the same as in an ordinary pipe organ. To this end, the switches 54 lFig./14 are interposed between the sounding switches 43 of the keyboard and the respective pick-up coils 18 for producing notes of one tone quality and similar switches 62 are interposed in conductors 53 for establishing short-circuits around the respective coils I8. Thus, it will be observed that by closing one or the other of the switches 54 and 62, a short-circuit will be established around the coils 54 or the coils I8 and the coil thus short-circuited will not -be effective to produce a note when the sounding switch 43 is closed and the coil not so shortcircuited will be active in producing sound of a tone quality corresponding to the construction of its core. By multiplying the number of such stop switches and pick-up coils, any desired number of different tone qualities may be obtained.

In order that the stop switches for producing the same tone quality under the control of different keys may be actuated by the same tab 24, these switches may be constructed as shown in Fig. 13, their contacts being mounted upon spring arms 65 which normally tend to close the switches. One arm of each set projects into operative association with lugs 65 on a reciprocable bar 61 maintained by a spring 68 into engagement with a cam surface 89 on the tab 24. By swinging the tab about its pivot "I0 between two limit positions determined by a detent II, the tone switches 54 may be closed and opened simultaneously and the corresponding set of pick-up coils withdrawn from and placed within the control of the keyboard operated switches.

To illustrate the simplicity of the construction required to produce any given number of different notes in accordance with the present invention, reference will now be made to Figs. 3 and 4 which show a unit capable of producing all of the notes in three full octaves of the tempered scale. Two of the disks, numbers 20 and 20 have nine rows of holes 28 containing 18, 24, 27, 36, 48, 54, 72, 96 and 108 holes while the disk 20 has rows with simiiar numbers of holes and an additional row with 17 holes. The other disk 20 has rows with 17, 18, 27, 34, 36, 54, 68, 72 and 108 holes respectively. The shaft 38 turns at 1800 R. P. M. and drives the disks 20 and 20 through gear reductions 31 of 16 to 59 and 10 to 31 respectively. The disk 20 is driven through an 11 to 43 gear reduction while the reduction for the disk 20 is 7 to 23.

It will be apparent that the different disks 20 are rotated at speeds bearing approximately a definite proportion to the frequencies of a plurality of notes of the tempered scale so that by providing a certain number of holes in the different rows on the disk, frequencies are obtainable which are substantially equal to those of the notes of the tempered scale, the variations from the exact frequencies desired being negligible.

The generator constructed as above described is adapted to produce thirty-seven different frequencies comprising the notes of the tempered scale extending from 130.5 (the octave below middle C) to 1044 cycles (two octaves above middle C). To produce the other notes controlled by the conventional organ keyboard, additional disks and pick-up coils would be required but much of the equipment would be duplicated simply by varying the drive ratio for such disks. For example, by halving the speed of rotation of any of the disks 20, each note produced thereby would be one octave lower. It will be apparent therefore that the number and different. kinds of the disks required to produce the notes of a full keyboard has been reduced to a minimum in the present invention and no additional disks are required in order to produce the different tone qualities in the manner above described.

Where, as in the present instance, the instrument is adapted to be controlled from several keyboards, the pick-up coils controlled by all of the keyboards are nevertheless arranged in series relation for the reasons above mentioned although different groups of the coils may normally be associated with certain of the keyboards. Fig. 15 is a wiring diagram of such an arrangement, only the circuits for producing three notes of two different tone qualities under the control of keys 2I 2I U of the great manual, three notes of two different tone qualities under the control of the keys 22 22 22 of the swell manual, and three notes under the control of pedals 23 23 23 being shown. It will be understood, however, that actually there will be one set of pick-up coils for each key or pedal of the three keyboards, the number of different tones of a given pitch being determined by the number of pairs of pick-up coils for each key. The pick-up coils controlled by the swell manual are numbered 72 and 13. Each pedal is adapted to render operative two pick-up coils 15.

The circuit for all of the pick-up coils grouped as shown in Fig. 15 extends from the amplifier I6 through a conductor I6 having the manually operable switch 49 therein through the successive by-pass switches and by-pass conductors H of the coils "I5 to a conductor I8 which in turn leads through the successive by-pass switches 42 of the swell manual. The by-pass conductors between the latter switches are represented by dotted lines I9 with the exception of by-pass con ductor for the switch of the key 22 which con-" prises a conductor having a normally closed by-pass switch 8| of the pedal 23 interposed therein and extending to a normally closed bypass switch 82 of the great manual key 2|. From the latter switch, the circuit extends through a conductor 83 and the by-pass switches 42 of the great manual keys and by-pass conductors 84 represented by dotted lines. The bypass for the switch 42 of the key 2| extends through a conductor 85 having interposed therein a normally closed by-pass switch 85 of the pedal 23 From the conductor 85 the circuit extends through the inductance coil SI and a conductor 8! back to the amplifier. It will be apparent that the different pick-up coils associated with the different keyboards may be rendered active by opening the proper stop switches 54 and 82 and depressing the proper keys. The sounding of any note, it will be observed, involves opening of a by-pass conductor and closure of one of the sounding switches 43 by which the circuit is shunted through the corresponding pick-up coil.

The circuit arrangement above described also illustrates how the pick-up coils normally controllable from one keyboard may be adapted readily for control from another of the keyboards. For example, by extending the by-pass for the pick-up coils I2 and I3 through the conductor 80 and the by-pass switch 8I of the pedal 23 this by-pass may be opened by depressing either the key 22 of the swell manual or the pedal 23 To enable the amplifier circuit to be extended through the coils I8 or 84 by depression of the pedal 23 the sounding switch 89 of the pedal 23 is arranged in parallel with the sounding switch 43 of the key 2I Thus when the pedal 23 is depressed, closure of the switch 89 and opening of the switch 86 extends the circuit through the pick-up coils I8 or 64 depending on which of the stop switches 54 and 82 is closed, and 1 opens the by-pass thereby sounding the corresponding note. To render the pedal 23 ineffectual in thus controlling the coils I8 and 84, a. short-circuiting switch 98 may be closed. Similar pedal-controlled circuits may be associated with any number of the coils of the great manual with all of the short-circuit switches 90 arranged for actuation by a common one of thetabs 24.

The coils normally controlled by any one of the keyboards may be adapted for control from both of the other keyboards. This is accomplished, in the case of the pick-up coils 12 and 13 of the swell manual, by interposing by-pass switches 82 and BI of the great manual key 2| and the pedal 23 in series with the by-pass switch 42 of the swell manual key 22 and arranging the sounding switches 9| and 92 of the key 2| and the pedal 23' in parallel conductors 93 and 94 thereby placing these sounding switches in parallel with the sounding switch 43 of the key 22 With shortcircuit switches 95 and 96 both open, it will be apparent that the coils l2 and "I3 may be thrown into the amplifier circuit by depression of the pedal 23 or either of the keys II and 22 Other similar circuits, here omitted for simplicity of iilustration, are employed to permit other of the coils of the swell manual to be controlled from the great manual or the pedals.

Variable resistance shunts 91 and 9B,similar to the shunt 55 above referred to may be employed as volume controls .for the swell manual and the pedal keyboard. These shunts together with the shunt 55 may be actuated from pedals 99 of the console. A similar shunt I08 controlled by one of the pedals 99 is arranged to control the volume of the combined output of all of the pick-up coils. If desired, a conveniently operable switch I may be provided to short-circuit the pick-up coils I and thereby withdraw these coils from control by the pedals.

To enable the notes to be sounded with a tremolo effect, a transformer IOI (Fig/) is rendered active by opening of the switch 49 and closure of switches I02 and I03, all of which may be combined in a double-pole double-throw switch. Opening of the switch 49 interrupts the connection between the pick-up coil circuit and the amplifier and closure of the switch I02 connects the pick-up coils in series with the primary I04 of the transformer. At the same time, closure of the switch I03 connects the transformer secondary I05 in the input circuit of the amplifier. Interposed in the circuit of the transformer is a rotor I06 driven from the motor 35. This rotor is composed of magnetic material and has annularly spaced teeth I01 defining low reluctance sections with intervening sections III!' of substantially higher reluctance, so that in the rotation of the rotor, the reluctance of the magnetic circuit through the transformer will be varied at a frequency determined by the number of the teeth I01 and the rate of'rotation. Thus, a tremolo effect of predetermined frequency will be produced in the notes which are sounded as a result of depression of the different keys, the voltages produced by the pick-up coils being impressed upon the amplifler; by induction through the transformer windings.

It will be apparent that the musical instrument constructed in the manner above described is capable of producing all of the notes of the tempered scale and in a widevariety of tone qualities thereby simulating; the results obtained with an ordinary pipe organ. However, theconstruction is much simpler and more compact owing to the fact that the entire instrument comprises a relatively small number of differently shaped parts all of which are simple to manufacture and most of which canbe formed from sheet metal. The instrument is rendered posi tive and reliable in operation by virtue of the novel arrangement of circuits employed.

I claim as my invention:

1. In a musical instrument of the character described. the combination of a disk composed of magnetic material and perforated with holes arranged in concentric rows containing 18, 24, 27, 36, 48. 54. 72, 96 and 108 holes respectively, a plurality of constantly energized magnetic cores each exposed to the holes in one of said rows. means for rotating said disk ata constant speed bearing a fixed relation to the frequency of a note of the tempered musical scale, electromagnetic coils in which voltage pulsations are induced by variations in the reluctance of the magnetic circuits through the respective cores. and means for reproducing acoustically the voltage pulsations in said coils.

2. In a musical instrument of the character described, the combination of a disk composed of magnetic material and perforated with holes arranged in concentric rows containing 1'7, 18, 2'7, 34, 36, 54, 68; 72 and 108 holes respectively, a plurality of constantly energized magnetic cores each exposed to the holes in one of said rows, means for rotating said disk at a constant speed bearing a fixed relation to the frequency of a note of the tempered musical scale, electromagnetic coils in which voltage pulsations are induced by variations in the reluctance of the magnetic circuits through the respective cores. and means for reproducing acoustically the voltage pulsations in said coils.

3. In a musical instrument of the character described, the combination of a rotatable member carrying an annular row of magnetic and nonmagnetic sections alternately arranged in endto-end relation, means for rotating said member at constant speed, a constantly energized magnetic circuit including two magnetic cores having opposite end faces adjacent and on opposite sides of said sections, a pair of electromagnetic coils each linking one of said cores adjacent said member, and means responsive to the voltage pulsations in said coils for producing sounds of corresponding frequency.

4. In a musical instrument of the character described, the combination of a device responsive to alternating voltages to reproduce sounds of corresponding frequency, a permanently energized magnetic circuit having two alined cores with opposed ends defining a narrow air gap in said circuit, a disk of magnetic material rotated at constant (speed and projecting transversely of said cores into said air gap, means for rotating said disk at constant speed, an annular row of circumferentially spaced holes in said disk spaced radially from the diskaxis the same distance as said cores. an electromagnetic coil linking said circuit, and means for impressing the alternating voltage induced in said coil upon said device.

5. In a. musical instrument of .the character described, the combination of a rotatable member.

carrying an annular row of sections of relatively high and low reluctance alternately arranged in end-to-end relation, 1 means for rotating said member at constant speed. means providing a constantly energized magnetic circuit extending through said sections and including two alined parts disposed on opposite sides of said member, two electromagnetic coils connected in series relation and each linking said magnetic circuit. and means" responsive to the alternating voltage induced in said coils and operable to produce sounds of corresponding frequency.

6. In a musical instrument of the character described, the combination of a device responsive to alternating voltages to reproduce sounds of corresponding frequency, a rotary disk of magnetic material having an annular row of perforations therein, a constantly energized magnetic core having one end disposed adjacent and facing said row of holes whereby rotation of said disk produces alternating variations in the reluctance of the magnetic circuit through said core, an electromagnetic coil enclosing said core and arranged to impress upon said device the alternating voltage induced therein, and means operating automatically to compensate for lateral wobbling of said disk and maintain uniform the amplitude of said alternating voltage.

7. In a musical instrument of the character described, the combination of a device responsive to alternating voltages to reproduce sounds of corresponding frequency, a rotary disk of magnetic material having an annular row of perforations therein, an electromagnetic coil associated with said device, and means providing a magnetic circuit extending through said coil and said disk at the radius of said holes and acting, during rotation of the disk, to induce in said coil an alternating voltage which is maintained uniform in spite of lateral wobbling of the disk.

8. In a musical instrument of the character described, the combination with sound-producing means including an amplifier of an arm, a pair of arms cooperating with said first arm to form two switches, said first mentioned arm normally tending to move in a direction to maintain one of said switches closed and the other normally open, a manually operable device by which said first arm may be moved in a direction to open the normally-closed switch and close the normally-open switch, and a pair of stops operable upon said second arms to cause opening of said normally-closed switch subsequent to closure of said normally-open switch upon movement of said first mentioned arm in one direction and closure of the normally-closed switch prior to opening of the normally-open switch upon movement of the first arm in the opposite direction, an electromagnetic coil arranged in series with said normally-open switch and a conductor interposed in the input circuit of said amplifier and in parallel with said coil and the normally-open switch, said conductor having said normally-closed switch interposed therein.

9. In a musical instrument of the character described, the combination with an amplifier of means for impressing voltage pulsations upon said amplifier comprising a normally-closed series circuit, a plurality of pick-up coils in which voltage pulsations are induced, and selectively operable means by which one or more of said coils may be introduced in said circuit while maintaining the same closed at all times.

operable devices each associated with one of said normally-open switches and the associated normally-closed switch and operable upon movement out '01 normal position to close the normally-open switch and thereafter open the bypass switch.

11. In a musical instrument of the character described, the combination of a device responsive to alternating voltages to produce sounds of corresponding frequency, a plurality of pickup coils, means to induce voltage pulsations of audible frequencies in said coils, normallyclosed by-pass conductors in the input circuit of said device each arranged in parallel with one of said coils and having a switch interposed therein, and a plurality of selectively operable devices each arranged to actuate one of said switches.

12. In a musical instrument of the character described, the combination of means providing a plurality of magnetic circuits through which magnetic flux constantly threads, means for varying the reluctance of said circuits at different audible frequencies, a plurality of coils each linking one of said magnetic circuits, an electric amplifier, a constantly closed input circuit for said amplifier, selectively operable means by which any one or more of said coils may be connected in series relation in said amplifier circuit, and means associated with the output circuit of said amplifier for reproducing acoustically the wave form impressed upon said amplifier by the combined action of coils in said circuit.

13, In an electric musical system, the combination of a plurality of electromagnetic pickup coils connected in series relation, a plurality of conductors each forming a shunt around one of said coils and having a switch interposed therein, a sounding switch connected in series with all of said coils, a by-pass conductor in parallel with said coils and all of said switches and having a normally closed switch interposed therein, selectively operable means for opening said by-pass switch and closing said sounding switch whereby to extend a circuit through one or more of said coils according to which of said first mentioned switches is open, an alternator for inducing alternating voltage of a predetermined frequency in all of said coils, and. an amplifier having said by-pass conductor interposed in its input circuit.

14. In a musical instrument of the character described, the combination of an electromagnetic coil, an alternator for producing an alternating voltage in said coil, a plurality of normally open switches arranged in series with said coil and in parallel with each other, an amplifier having a normally closed input circuit with a plurality of switches arranged in series therein and in parallel with said coil and said normallyopen switches, a plurality of manually operable keyboards each having a key adapted when depressed to close one of said normally-open switches and open one of said normally-closed switches whereby said coil may be interposed in said circuit by depressing any one of the corresponding keys on the different keyboards.

15. In a musical instrument of the character described, the combination of an electromagnetic coil, an alternator for producing an alternating voltage in said coil, an amplifier, an input circuit for said. amplifier having interposed in series therein a plurality of normally-closed switches arranged in series with each other and in parallel with said coil whereby the by-pass around said coil may be interrupted by opening any one of said switches, and a plurality of keyboards each having a key arranged to actuate one of said switches.

16. In a musical instrument of the character described, the combination of a member rotatable at constant speed and carrying an annular row of sections of alternately high and low magnetic reluctance, a plurality of magnetized cores exposed to said sections whereby the flux threading the cores is varied periodically, the magnetic circuits through said cores having different physical characteristics, a pick-up coil for each of said cores in which voltage pulsations are induced, and sound-producing means arranged to respond to the voltage pulsations in the different coils.

1'7. In a musical instrument of the character described, the combination of a plurality of magnetized cores, a plurality of electromagnetic coils each linking the magnetic circuit through one of said cores, constantly operating means for producing periodic fluctuations in the reluctance of each of said magnetic circuits and corresponding alternating voltages in the respective coils, said circuits having different physical characteristics whereby to produce corresponding variations in the wave form of said voltages, means for reproducing acoustically the wave forms of said voltages including an ampliher, and selectively operable means for impressing any number of said voltages upon said amplifier.

18. In a musical instrument of the character described, the combination of a rotatable magnetic member having an annular row of nonmagnetic sections therein oi the same crosssect'ional shape, a "permanently magnetized core projecting toward said member with one end terminating opposite the path of movement of said non-magnetic sections, the cross-sectional shape of the end of said core being different from the shape of said non-magnetic septions, a pick-up coil linking said core, and a sound-producing means responsive to the alternating voltage inpath of movement of said non-magnetic sections,

the dimensions of the end face of said core being different than that of each of said non-magnetic sections, an electromagnetic coil linking the magnetic circuit through said core, and sound-producing means responsive to the alternating voltage induced in said coil upon rotation oi! said member.

20. In a musical instrument of the character described, the combination of a plurality of electromagnetic coils, a plurality of magnetic circuits each linked by one of said coils, a common means operable to produce periodic fluctuations of substantially equal amplitudes and the same frequency in the reluctance of each of said circuits whereby to produce alternating voltages in the diilerent coils, said magnetic circuits having difierent predetermined physical characteristics whereby to impart diiierent wave terms to the voltages induced in the difierentcoils, and means responsive to said voltages and operable to reproduce acoustically the wave forms thereof.

21. In a musical instrument of the character described, the combination of a rotatable plate composed of magnetic material and having a circle of round holes of equal size formed therein, a plurality of magnetized cores having ends oi. different cross-sectional shapes disposed adjacent said plate opposite said holes whereby the reluctance of the magnetic circuit through each of said cores is varied periodically in the rotation of said plate, a plurality of pick-up coils each associated with one of said cores and having an alternating voltage induced therein of a frequency determined by the speed of rotation of said plate and the number of holes in the circ'e and of a wave form determined by the crosssectional shape of the core, and sound-producing apparatus responsive to the combined voltages induced in any one or more of said coils.

22. In a musical instrument of the character described, the combination of a disk of magnetic material perforated to form an annular series of equally spaced holes, a pair of constantly energized magnetic cores having their ends disposed adjacent said disk opposite said holes, a pair of pick-up coils each linking the magnetic circuit through one of said cores, an electrical device adapted to respond to the alternating voltages induced in said coils and to produce sounds corresponding to the wave forms of said voltages,-

said cores having different dimensions whereby to produce voltages of diiferent wave forms in said coils.

23. In a musical instrument of the character described, the combination of a plurality of constantly energized magnetic cores, means for moving across the end face of each of said cores a magnetic member having alternately arranged magnetic and non-magnetic sections producing alternating fluctuations in the reluctance of the magnetic circuits through said cores, a plurality of pick-up coils associated with the respective cores and having induced therein alternating voltages corresponding to said reluctance fluctuations, the ends of said cores exposed to said sections being of different cross-sectional shapes whereby to vary the wave forms of said voltages, and sound-producing means responsive to said voltages and operable to reproduce acoustically the wave forms thereof.

24. In a musical instrument of the character described, the combination of an electrically operable device responsive to alternating voltages to produce sounds of corresponding frequency, a rotary disk composed of magnetic material having a plurality of concentric rows of holes therein, a constantly energized magnetic core having one end disposed adjacent said disk and bifurcated to form two end faces each exposed to the holes in one of said rows, and an electromagnetic coil linking the magnetic circuit through said core and electrically associated with said device.

25. In a musical instrument of the character described, the combination of an electrically operable device responsive to alternating voltages to produce sounds of corresponding frequency, a rotary disk composed of magnetic material having a plurality of concentric rows of holes therein. a constantly energized magnetic core having one end disposed adjacent said disk with its 'end face overlapping the holes in a plurality of said rows, and an electromagnetic coil linking the magnetic circuit through said core and electrically associated with said device.

26. In a musical instrument of the character described, the combination of a transformer having primary and secondary windings and a rotary member interposed in the magnetic circuits of the transformer. said member having alternately arranged circumferential sections of high and low reluctance, means for rotating said member at constant speed, sound-producing apparatus in-. cluding an amplifier having an input circuit adapted to be connected to said secondary winding, an electromagnetic coil adapted to be connected in series with said primary winding, and an alternator for generating in said coil an alternating voltage of a frequency within the range of audibility.

27. In a musical instrument of the character described, the combination of sound-producing apparatus including an amplifier, a transformer having its secondary winding adapted for connection in the input circuit of said amplifier, an

electromagnetic coil adapted to be connected in series with the primary winding of said transformer, an alternator operable to induce alternating voltage in said coil, and means for varying periodically the magnetic coupling between said windings.

28. In an electric music system, the combination of an electromagnetic coil, an alternator for producing in said coil an alternating voltage of a frequency corresponding to a note of the musical scale, a transformer having primary and secondary windings, means operable to vary periodically the magnetic coupling between said windings, sound-producing apparatus including an amplifier, switching means by which said secondary winding may be interposed in the input circuit of said ampifler, and switching means by which said coil may be connected in said input circuit or in series with said primary winding.

EDGAR D. LILJA. 

